Unconstrained supply plan stuck at refreshing data stage and not completing

we have created a supply plan which is stuck at refresh data stage and not progressing. Checking from backend we could see snapshot entity is running for almost 14 hours and not completing. This is a unconstrained plan with horizon 900 days as requested by business , volume of data is also very high with 10 orgs and almost 23 million items. we set pegging calculation days as 300 .

Can someone confirm if this is because of large volume of data or anything else we have to check and correct here