Assuming that late may in an average year is comparable to mid june in a high snow year, I'd be inclined to think that you'll be ok. I can't say that it's "safe", it's NOT. Backpacking isn't safe, and snow travel is much less so.
I hiked the PCT through the sierra in June of a heavy snow year. Most people said it was "impossible", "suicide", etc. We all had a superb time. Going before the pack adds some specific complications though.
You'll be making your own trail. It was safer for me because i could often hike in preformed steps. You'll have to do the correct navigating and more walking on virgin, slippery snow.
Stream crossings could be even higher than the very high levels that I saw. Multiple thruhikers got swept away in fast moving current. No one was seriously hurt in the swims, but they're "near misses".
The biggest obstacle *might* be Forester Pass. You WILL have to cross a steep snow slope that has high fall potential and deadly consequences. It's likely that there won't be prints for you to walk in. One year, early thruhikers even had to boot up the entire couloir, cut through an overhanging cornice at the top of it, and scurry to the top. That is by no means the conventional crossing of Forrester Pass. It's HIGHLY DANGEROUS. Insane without crampons. Extremely unwise without mountaineering experience. It's highly likely that no one will be able to give you beta on whether Forrester has been crossed, weather the trail is melted out, whether you'll be climbing the steep snow couloir the whole way, whether there is a cornice at the top of it.
If you hit all the wrong notes, the snow won't be fully consolidated and you'll have an excessively hard postholing hike ahead of you.
Should you do this with no experience? No of course not. But it would be an adventure! Mentally preparing yourself won't help when it comes to learning how to snow climb, assess objective hazards, cross flooding creeks, use crampons or ice axes.
Better advice could be received from guys that have hiked the Sierra in May. Scott Williamson and Trauma are the only one I know that fit the bill.