Join Date: Oct 2013
Location: Chilliwack, BC, Canada
I'd start with setting static sag and race sag. Once the sag is correct, you will have a good starting point for fine tuning. Adding air can be helpful for a temporary remedy but usually best to rely on less variable effects, IMO. Too much air pressure from pre-pressurization or suspension compression is likely to blow the fork seals.
If you are wondering about using a higher oil level than standard, that will increase the compression ratio of the air in the shock and act like a stiffer progressive spring. Too high oil level will result in hydraulic lock which will make the suspension bottom out too early.
Adding spacers is the usual way to set sag but one needs keep in mind that the ultimate spring rate does not change so the spring will coil bind under too much load as before.
IME, the best way is to take an educated guess as to oil viscosity so 15 wt sounds like a good try for a heavier guy. You will be able to work that to a finer setting later. First is sag, then find a section of typical riding you do. Ride the section many, many times until you have it down pat and it's becoming boring. Then make a change to see whether your timed ride of the section is better or worse, then make a change and evaluate.
At 5' 7" and 170 pounds, you aren't going to receive ridicule from this quarter. ;-)