If you want to stay in the $500 price point (about what I see the Bushnell 5-15 going for) there are a few good options out there to pick from. If you want more magnification the Vortex Viper line would be a good one. You can get a 6.5-20x in your budget. Weaver has a couple options that fit. Their Grand Slam line will get you into a 6-20x model or a Classic V 6-24x. You could also grab a Sightron SII 6-24x for that price, but not quite the BigSky SII. You would be right on the edge of a Nikon Monarch 5-20x but about $100 off the 6-24x. It will also get you into a Leupold VX-II 6-18x. You will be just a little short of a Burris Fullfield Tactical 6.5-20x. It will even get you into a Bushnell Elite 6-24x.
All of these scopes are quality scopes from a decent manufacturer. Some have slightly better features here or there but they are all quality built. I don't want to point you away from the Bushnell Tactical if that is what you really want. I just want to let you know that in the budget you have set for the scope, you can get more magnification without spending more money, yet still keeping quality. Some of those scopes are better built or better optically than others, but they all are in the ballgame. Most of those also come in a 4.5-14 or similar magnification range for a bit less money as well, which would save you some over the Bushnell.
When you look at the specs of the Bushnell Tactical, it looks to be basically their old 3200 line (their 3x erector) with externally adjustable turrets. It's only a 1" tube for a tactical style scope, and it's limited to 40 MOA of internal adjustment. That number isn't horrible for a casual shooter (myself included), but if you want to play at long range, more adjustment is very beneficial. When compared to the Viper mentioned above, the Viper has 68 MOA of adjustment, and while the turrets are covered, when the covers are removed they are easily hand adjusted.
I believe the Bushnell Tactical line to be on the same glass/coatings as the 3200 line, which would put it in the 92% light transmission range. The Viper, Monarch, SII, and standard Bushnell Elite all are at the 95% mark, which is what you see in scopes the next price point up. It isn't a huge difference, but it is like going from the old Elite 3200 to the 4200, the Buckmaster to the Monarch, or the VX-II to the VX-III, which some people find as a must.
The big drawback for the Nikon for me is the amount of internal adjustment (again only important if you plan to shoot mid range as well as long range). It only had 34 MOA of adjustment. The standard Bushnell Elite is even worse at only 26 MOA of adjustment.
Looking at the ballistics of your rifle, a 175gr SMK driven at 2700fps has a little over 25 MOA of drop from 500 yards out to 1000 yards. If you plan to shoot from 500-1000 yards only, a scope like the standard Bushnell Elite would have to have a lot of luck to work. You would need to find a scope base/elevation adjustable rings that put the zero at 500 yard near the absolute top of the adjustment range. Then, at 1000 yards, you would be at the absolute bottom of the adjustment range. The problem here is that you get the best image through the center of the optic and pushing it to one extreme or the other gives a degraded image (though how much depends on the quality of the scope). You have no room to shoot any closer as you are out of adjustment outside of the 500-1000 yard range.
With 40 MOA of internal adjustment on the Elite Tactical, things are a little more friendly, and if you use the right bases/rings, you can adjust elevation from 0-1000 yards all on the scope. Again though, you will be looking through the extremes of the adjustment and you will have to rely on some correction in the bases/rings for elevation to get you to fit in the range.
When you look at the Viper and it's 68 MOA of adjustment, you can basically toss it on any standard ring/base combo and be able to adjust out to 1000 yards. Also, if you put it on a base/ring combo of around 15MOA of elevation, you will be working on bit closer to the center of the lens through the entire adjustment range, which should provide a better image.
There is a lot to go into picking a scope. Make sure you know what you're getting before you buy, especially if you plan to spend $500. Some scopes have features/specs that make them much more desirable for a given style of shooting.
