The 6150RF and 5881ENM are very similar. Both are 16 zone receivers, both are for use with 5800 series ademco equipment. The 6150Rf receiver is built into the keypad so you obviously get a keypad out of the deal, but it is more expensive. The range of either would be good for a residential application. The downside is that if the keypad in the 6150RF goes bad, you lose the receiver also. It does not matter v15p or v20p, same deal.
Normally my company uses a 5881enl receiver for applications up to 8 wireless zones, and we use a 6150rf for new installs for 9-16 zones. If we are expanding on a system and we need 9-16 wireless zones, we use the 5881enm.