I think I would use a cannister filter if you want to hide everything. If you don't love the fluval ones you could try another brand, maybe even with an output spray bar.
I don't see how you could get away from a canister if you want minimal intrusion in the tank. I've seen some really cool looking small canisters on eBay. If you want good old school proven stuff, go with an eheim 2213.
I think they're aquael, i've wondered whether it'll heat up the 15 gal fully, but given the low temp needs of the fish and shrimps; i don't see it being a problem^ i think i've had one of those heaters before, arent the called stealth heaters or something???
Also for filters, maybe check out a brand called Eden, they arent too expensive over here and mine havent caused me any problems except for the need to change out the seal around the lid one time after 2 years of use...
Seen that one too, looks promising; but it's the quality i'm a little wary of quite truthfully. Ideally I think eHeim is the answer, even one of the smaller models