Under this formula, a participant no longer is credited with additional service after 10 years of service. At 10% per year that means their accrued benefit is equal to 100% of their average compensation after 10 years of service. They will most likely still have increases in their accrued benefit after year 10, not due to additional service, but due to increases in average compensation.
Lump sums in DB plans are subject to the 417(e) minimum. If the employee's average pay was $75,000/year, that's $6,250/month, which would be equal to their accrued benefit if they have 10 years of service. My software tells me that the present value factor using the 2022 applicable mortality table and the October 2022 segment rates, for a participant currently age 47 with normal retirement age 65, is 52.571. $6,250 x 52.571 = $328,569.
The actuary should be able to explain how they came up with the $315,000 number.