I'll start by saying that the TM15 is definitely the better choice in my opinion in terms of the marker as a whole. I assume we're comparing it to the Elite version of the BT G36 seeing as the two are around the same price.
The main thing you'll get from the TM15 over the G36 Elite is the electronic firing modes and such.
Internally, the TM15 is practically an Invert Mini with a milsim body over the top of it. On the other hand, the G36 Elite is essentially a BT4 Slice which means that its not going to have any firing modes or other features associated with electronic operation.
Somethings you do get with the ELITE version of the G36 is the Rip Clip and the Apex barrel.
The ripclip basically means that you'll get an electronic hopper for your paintballs along with the marker. This is pretty nice as it means you won't need to buy an electronic hopper later on if ever. If you were to get the TM15 it would operate just fine with a cheap gravity fed hopper however it would need a more expensive electric hopper to ideally keep up with those electronic firing modes, it's not essential for them.
The Apex barrel is pretty nice. This barrel has a tip on it which allows you to curve your shots around corners or fly further. Bare in mind that this can be bought separately for just about every other marker that exists so if you got the TM15 you could buy this separately later.
In conclusion, it may seem like you get more for your money from the G36 Elite however the TM15 will always shoot a lot better as it has far better internals. You may want to buy an electronic hopper in the future for the TM15, possibly a barrel later on. But even from the beginning with a gravity fed hopper, the TM15 comes out ontop in terms of quality and performance.
Hope this helped
