I LVoe the 15! It's perfect for smaller bags and it holds a considerable amount. I have the 15, 19, a cosmetic pouch and a mini pochette and I LVoe them all.
My current collection is listed in my signature, I've been collecting since 2011.
Oh and these are bags I sold (I re-purchased the bloomsbury)
Galliera PM
Delightful MM
Cabas Beaubourg
Neverfull MM Mono
Neverfull MM Ebene
Westminster GM
Bloomsbury PM
Menilmontant PM
Odeon PM
Speedy B 30
MC pochette
DE mini pochette
Pomme Vernis Zippy Coin Purse
Azur pochette
Wapity
Mono Eva
DE Eva
Mono Speedy 35
Can I ask...what did you not like about the Westminster GM? This is the handbag I'm considering next. Would love your opinion. Thx!