We are using Adobe DTM for adding tags based on onload or onclick events. Now we want to determine how adding tags will effect page's performance? For a specific page, say on "contact us" page of a website, adding 3 tags will give same load time compared to adding 50 tags (adding tags on load event)?
There are a number if browser plugins you can use to measure page performance in addition to the built in inspector tools that most browsers have. The increase in load time will depend on which tags are being added and how heavy the tag is. Try adding the tags in staging and measuring with one of the browser extensions.