High IO delay in LXC but not in VM

[zero.]

Hello,
I've been using a VM for torrenting, and the performance was okay, with I/O delays around 0.1% to 1%.
When I tried to recreate the VM in a new LXC (unprivileged), to my surprise, the I/O delay increased to 15%. I'm doing exactly the same as I did in the VM, using the same hard drive to store the downloads.
What am I doing wrong?

 

[zero.]

Is it possible that the VM has similar performance but does not print the I/O delay on the dashboard?