Problem with performance. Maybe transaction log problem?

Hello,

we have ETL process which starts everyday. I noticed that load time started to become bigger. Since no changes hasn't been made for weeks I think that it could be related to transaction log.

Database recovery model - Simple. Database size 110GB, transaction log size 25GB.

Also these parameters: SQLServer:Databases - Log Flush Wait Time, SQLServer:Databases - Log truncations now are bigger than they was.

Would transaction log truncation help in such situation?