Dada2 denoise - why do I have so many reads filtered out

I see..but I still have doubts. Please check the results of default setup (Q2)

sample-id input filtered denoised merged non-chimeric % left
#q2:types numeric numeric numeric numeric numeric
LB17-16-001 145783 123434 123434 68005 45408 31.15%
LB17-16-002 70462 60081 60081 31014 22621 32.10%
LB17-16-003 119707 96946 96946 73652 30813 25.74%
LB17-16-004 130350 112151 112151 61758 42091 32.29%
LB17-16-005 111168 95150 95150 50107 35143 31.61%
LB17-16-006 122771 99810 99810 68519 38149 31.07%
LB17-16-007 119037 100004 100004 60282 34820 29.25%
LB17-16-008 105227 83766 83766 51094 24924 23.69%
LB17-16-009 203605 171129 171129 85039 50089 24.60%
LB17-16-010 143034 121132 121132 105902 44471 31.09%

Is it a lot?