When we make updates to email templates (such as a change to a subject line, for example), we do not see these changes get reflected to the emails or workflows that are built off of the said template. We need to remove the email from the work flow and add it back in to get all of the updated attributes from the updated template.
When we have 16+ workflows all using the same template, we need to update each of the emails/workflows individually to get the latest version of the template.
If you are using recurring delivery then I am afraid there are no other options as per my knowledge . As when we create a delivery using template we are creating a duplicate from template and any changes in template will not reflect in delivery .
You can try to use continuous delivery as an alternative if it's suits your requirement as in continuous delivery you don't have to delete and create new one every time just Re select the template.
When you attach a delivery template to a recurring delivery and save it, a new delivery template is created with same name but different internal name (obviously). You can try to mass update the delivery templates that are created after attaching them to a recurring delivery. This can be done by selecting the templates to be updated (In your case select the delivery templates created by recurring delivery), right click on selected list > Actions > Mass update of selected lines (check screenshot below).
When you select this option a console will open that will display a list of columns. These columns are related to various properties of the template. You can play around and find the concerning columns that correspond to the fields that you are willing to update/change (Find screenshot below). Once you select a column, you can insert the value that you want to update in the value field.
Continue with the steps accordingly and all the selected templates will be updated with the required values. Although there are some fields that might not be available in this list, but most of them can be found here.