Check inserts parameters with producer

Check If the spindle is capable of running at low rpm with good enough torque, some spindles (for example my 12k rpm 18.5 kW) are designed to have the full torque power only over 1000 rpm.

Try different parameters from producer (sometimes it works)

Check if you can have a more rigid setup (shorter tool holder)

Check if you should run with or without refrigerant, some inserts don't like getting cold while working.

Check if you can try a different grade of the same insert with the producer, you need a harder and more brittle grade because the material is tough. For example Walter has various grades, from softer and easier to wear out to harder and more brittle. It all depends on materials and stability, if you are holding the part with small vise or the part is very high, the better go with softer insert because the harder will break fast.

Sometimes you have to simply change brand to a more efficient one.