My last observing night M4 and Omega Centauri where at same distance of horizon (21:30H at 29°S) and placed in fairly equal light polution places (a bortle 4 sky). Unfortunately I don't have the 15X70, even in 15X85 or 10X50 Omega centauri had an apparent diameter 5 to 6 times more than M4 (at my eyes).

I looked by info on them, to check if my observation was correct, it's very curious, the citation there is of about almost the same apparent dimensions for the two (36' M4 and 36,9' OC) I think this difference I observed should be related to apparent magnitude them (7,12 M4 and 3,7 Omega Centauri).

OC was visible naked eye, unaided, it was about half the size of M4 in the 10X50.