Trying to decide between a TTHP 36" 15 KAW or a TTHP 48" 17 KAW. Already have a Lazer Z HP 44" 17 KAW. Will have both within 3 years just trying to decide which to get first. Will the 4817 have as good of cut as the 3615 with respect to the amount of HP to inches of cut? Do the 15 and 17 KAWI's have interchangeable maintenance parts... such as fuel filters,oil filters,air filters,plugs,etc.? Thanks for any input!