Unfortunately, the extra protection comes at a cost. Google Chrome team member Charlie Reis reveals the new security features will increase RAM consumption by an extra 10 to 13 percent:
All this sounds good, but it comes at a cost. Reis highlighted that Site Isolation will chow down on an extra 10 to 13 per cent total memory overhead in "real workloads", basically making the Chrome browser an even bigger memory hog than it already is. But Reis did say Google is working on optimising Chrome to it keeps its security but runs fast.