Hello and welcome to you and Max from me.
Marje asked me to stop by, as I've experience with larger doses, as well as switching from Caninsulin (Vetsulin is same but rebranded in the US) to Lantus. I eventually switched to Levemir. When we switched from Caninsulin to Lantus, Neko was on 5 units of Caninsulin, and just seeing numbers in the mid 100's - usng a human meter. Her vet had us switch to 1 unit of Lantus. It took me over 3 months to get back to where we should have started Lantus at.

All the time Neko was in higher numbers than were necessary. And I still had to keep increasing her to her highest dose at 8.75 units. I'm glad you switched it to 5 units tonight.
The link to your previous post, for continuity:
https://felinediabetes.com/FDMB/threads/7-23-max-amps-2-521-6-327-10-484-shot-late.250260/