If you're thinking and tried "outbandwidth" on the interface, it wouldn't work as you expect if it's off-loading to asic. We had a similar question but not to IPSec interface, instead to wan1 on 60D and tried "set outbandwidth <kbps>" to find it doesn't work. TAC told us we had to set a policy specifically and disable asic off-loading, which would drop performance significantly. I think this is depending on the type of NPU or model. But likely the same with some other NPUs(60D has NPU4Lite).
So only practical option is setting up shaping-policies to control the outgoing traffic toward the IPSec interface.
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