Is a 660 Ti still a good GPU in 2015?

All depends on what games you play and intend to play in the future my friend! You're not going to be maxing out any newer AAA titles at 1080p, but it can most certainly hold its own playing most any games on lower settings. As far as that price goes, the new card retails for around ~360 so if that offer you're talking about is for a new card, I'd take it, maybe even flip it.
 


The 660ti is far more powerful than the GTX 750, I don't know where you got the idea that the GTX 750 is more powerful.
 


Well the 660 ti is pretty much on par with a 760. And I can run witcher 3 just fine at medium settings if I only use FXAA and turn post processing down. Here is a witcher 3 benchmark at medium settings and even includes the 660 ti it stays above 30fps and I bet it could do a lot better if they turned post processing down for that benchmark.

http://www.techspot.com/review/1006-the-witcher-3-benchmarks/page2.html
 
To answer your question in total, yes, a 660 ti will play most games with no issues at all. You may have some games requiring more power for the pretty things, but that's expected. Lower and take away a little of the pretty stuff and you'll still be able to play them and they'll still look fine.

And yes, $105 is a good price for the card.
 


Probably because I read 650 Ti...*shruggs* shit happens big difference, the 660ti was a Mid Range card $250 at launch so it should still be good for Medium to High settings.