When I try to filter only M+15 items to build combintions the site lists all Raid items on the chosen iLvl, and there is no way to filter only Raid items:
That picker controls which version of the M+ items show in the list (we only show one at a time so the list doesn’t get really long). Use the search/filter box above the list to filter it. For example, if you only want to see raid items, type “raid”, or only dungeon items, type “dungeon”. You can also search by item name, zone, boss, stats, etc.