High Log Flush Wait Time and filling Transaction logs
Usual supect, in this case: The IO subsystem is slow. Are you using SSDs?

DMVs are your friends. 

Identity &amp; Isolate Issues

Log Flush Wait Time


This is an indication of Underlying IO bottleneck 
What is the write latency?
Find out using sys.dm_io_virtual_file_stats &amp;
sys.dm_io_pending_io_requests


Size log files appropriately 


Your application seems to be a very high transactional load type.
If log files are frequenting to a certain size limit, it means it needs such size.
I would size my log files to be 750 MB if the log file is frequently reaching that size at its peak. 


Transactional log backups


Maybe you just need a more frequent log backup. 
Test &amp; decide.


As far as memory, a 30000 PLE looks good to me on a 32 GB RAM server. Assuming this is SQL's memory, not the server's. 

Resources:


Paul Randal's Transaction Log Monitoring 
Paul Randal's Page Life Expectancy