Should you keep the old data? Depends on how well the campaigns were run.
If you inherited a mess where all the ads campaigns were bidding for irrelevant keywords then the data of that account is not of much use.
However if the previous campains ran with some effectiveness then there is merit to keeping the account and not starting from scratch.
More info:
https://www.takesomerisk.com/ppc-audit-guide/
https://www.ppchero.com/inheriting-large-pay-per-click-accounts/
https://marketingtipbooks.com/tipbooks/inheriting-a-google-ads-account/
http://www.clixmarketing.com/blog/2017/11/09/how-to-approach-campaign-restructures/
https://e-m-marketing.com/2017/03/09/restructuring-google-adwords-accounts-more-efficient-case-study
https://www.wordstream.com/blog/ws/2017/05/02/adwords-account-structure-guide