Robert Snodgrass went to Norwich last season for a fee believed to be around £6million. In his final season at Leeds, he scored 13. In the Prem, he scored 6 and got 9 assists as he was one of Norwich's best players. It's worth noting that he was over 2 years older than Ince when he made the move.
Jay Rodriguez went to Southampton for roughly £7million. In his final season at Burnley, he scored 15. In the Prem, he scored 6 and got an assist. After a rocky start under Adkins, he played a key part in Southampton's solid season when Pochettino took over and changed his role. He was a year older than Ince when he made the move.
Adam Johnson made a big money move to Man City and got 6 goals and 6 assists. The next season with Sunderland he got 5 goals and 9 assists.
Even the likes of Routledge and Puncheon managed to get 5 goals and more assists.
My point is, that although the proposed deal is expensive, you shouldn't rule Ince out as a quality signing. All these are examples of players in similar positions coming into the Prem with worse Championship records, yet they succeeded, and in some cases thrived in the Prem.
Of course there's no guarantee that he'd do as well as those players for us, but looking at recent history of similar moves, there's every chance he can match or even surpass them!