Condition is everything. You could probably carry 75# plus your 150 lbs if the wheels are true, spokes properly tensioned and the hubs are good.

Strength is the least of your worries. Chromed steel wheels don't stop well in wet weather. Get (at least) a new front wheel with an aluminum rim. You can get a decent wheelset in 27" (or 700) from Harris Cyclery for about $130 with sealed bearings and aluminum rims. They also have ball bearing hubs for $100.

I give my steel wheels to people who leave their bikes at their beach houses.