Taking Delsym safe?

I bought 20, 15mg tablets of Dextrmethorphan HBr. I've taken a whole bottle of Robocough before and felt good before this was a year or two ago. Would it be be safe to take all 20 tablets? I weigh 210 and I'm 5'10. How do I do this do I just take them slowly? Not looking to do this again but would like to know