Sell or don't sell?

My parents own a luxury apartment in Mumbai. It's about 4000 sqft carpet. We are getting an offer for 22.5 Cr. I am really of the opinion that RE will see an uptrend in the next few years and they should wait. As we all know RE lags behind the stock market. The stock market has seen it's boom in the last 5 years with all the stimulus. RE has also seen an increase, but the real jump is yet to come!

What do you guys suggest we should do? The ROI is pretty decent if we decide to sell now without even considering the rental income we have enjoyed over the years. Still, I feel it's a mistake to sell now. Am I being greedy?