Database restore time increased after we changed from SQL Server 2014 to SQL Server 2016
For those who may have the same problem, we noticed that when we did the CHECKDB we had an error with PFS pages (https://www.sqlskills.com/blogs/paul/pfs-corruption-after-upgrading-from-sql-server-2014) and thus the solution was to correct these error with a DBCC CHECKDB(database_name, REPAIR_ALLOW_DATA_LOSS).
We also move the disk from 7K to 10K to upgrade performances.