According to the tables here: Suspension Springs and Sag- Ducati Up North
I think the spring on my shock should be OK for my weight in riding gear.
It's marked "1091-16/6.5" so, if I'm reading right, that means:
1091: the spring length is 160mm off the shock (it's 151mm on the shock, as my Haynes manual says it should be),
-16: 64 N/mm, and
6.5: a 6.5Kg/mm spring....(1kg is equivalent to 9.81 newtons)
With an all-up weight of around 175lbs, I should really have a spring rate of 7, but I reckon 6.5 is close enough to start with.
I think it'd probably be ok. Unless you're tracking the bike and looking for optimal performance, the Ohlins even if slightly undersprung will probably still perform much better than the stock unit. You may be able to offset the lower spring rate with some additional pre-load, but I'm not knowledgeable enough on shock tuning to say that's a fix or not.
For around town riding, you're probably just fine.
As an example, the Ohlins on my 748 SF has a 185lb spring on it. I weigh about 165 with gear, but the rear end of the bike is also about 1olbs lighter than stock too. I took a few mm of pre-load out and adjusted the compression down a bit, and turn up the rebound to help control the lighter weight.
Has been great so far and the bike feels very planted.
This is just my personal experience, and my situation was much more extreme so you'd probably be just fine. Let us know how it rides once you get it on there. They always need some fine tuning in the end, just play with it a bit making consistent runs along a known route after each adjustment. Will help you get a feel for how each adjustment is affecting the bike.