sp_BlitzFirst - Wait Stats Interpretation
So let's do a quick rundown of your top two waits:


IO_COMPLETION - waiting to write to storage
PAGEIOLATCH* - waiting to read from storage


In 30 seconds, your queries spent 1,655 seconds waiting on storage.

Your storage is probably slow - if you skip down to the next section in sp_BlitzFirst's output, it will show which data and log files SQL Server was waiting on, and for how long. However, before you leap to playing Pin The Blame On The SAN Administrator, consider:


Tuning indexes &amp; queries to reduce the amount of data read from disk (I'd suggest using sp_BlitzIndex and sp_BlitzCache for that, although I'm biased (disclaimer: I'm one of the coauthors))
Adding memory to cache data, which will reduce PAGEIOLATCH, thereby easing pressure on the storage, and will likely reduce the IO_COMPLETION waits too
Spending a whole lot of money on storage (you might guess that the above two fixes are above this one for a reason)