In Estonia transfers went from instant to slow after enforcing the SEPA payments. Same made transfers faster in other EU countries. Different starting points. Probably similar case in Finland.
Hmmm... the introduction dates would match me leaving from there, so that would be a possible explanation. On the other hand, the existing system was already using IBAN and stuff, so as an ignorant customer, SEPA looks like an acknowledgement of what was already in use, not requiring any change in the process. Dunno.
In your case, when you say slow, how slow has it become?
Bank transfers in Estonia did get slower when SEPA first arrived, but not horrendously so. I think the transfers used to be every 15 minutes and during most of the day. With SEPA it got downgraded to every hour and only during normal working hours. However nowadays we've already moved on to SEPA Instant Payments which take about 10 seconds and are EU-wide, provided the other EU bank isn't dragging its feet with implementing it.
In your case, when you say slow, how slow has it become?