I really think 15"s are too much on a roundie, but I'm a sissy.
For a narrow 14" option, why not buy a new set of these early Euro E30 wheels: STEEL RIM SILBER 5JX14 ET:35 P/N: 36 11 1 125 684
Check out these old posts:
http://www.bmw2002faq.com/component/option,com_forum/Itemid,57/page,viewtopic/t,325418/highlight,36111125684/
http://www.bmw2002faq.com/component/option,com_forum/Itemid,57/page,viewtopic/t,279542/highlight,36111125684/
I also have a newly restored and trued, professionally refinished set of early 13" tii wheels that are ready to go...I might sell them for the right price. These look very slick with the dog dish hubcaps.