15' is a pretty good distance. Though I'm a tower man myself, I'd recommend making certain that if you do switch it up to standmounts, that you have a plan for the sub.
Most towers on the market still aren't a substitute for a good sub, but if you are getting FR down to mid 30's, say, you might not really know what you're missing. Especially in music. But a standmount that might only hit upper 40's? You'll be missing a lot of info.
Perhaps with the upgrade, you can can get a better speaker quality in a particular line's upper tier standmounts... and still budget for the sub. (Hell, you should do that anyway!)