actions: Increase API request delay to 150 ms
Step 1 of T161284. Given that the median API response time (as measured
by the client) is ~115 ms  and the API response is artificially
delayed so that the preview starts fading in at 500 ms, we can increase
the API request delay to 150 ms without affecting the current UX while
decreasing the number of incidental HTTP requests triggered by the user
glancing their mouse over a link to another page.