Unfortunately for years Tauck literature has not done a very good job describing luggage restrictions.
How much over?
Your on-tour flights are on commercial carriers like LATAM, Avianca, and TAME, so you must first adhere to the airline weight and size restrictions. LATAM has 3 categories of "luggage"- Checked luggage, carry-on luggage, and personal item. The limitations are typically 17 lbs (LATAM) for carry-ons (Economy or higher) and 50 lbs (LATAM) for checked luggage. Note, the states, "The Basic fare does not allow carry-on bags". You'll need to call Tauck to see what fare class you'll be flying. We sat in steerage! but it could have been an Economy class fare when we did Peru & Galapagos a few years ago. The amount of space for carry-on luggage on the small regional aircraft (A319 is typical) flying this route is almost nil for anything but "personal items" - "purse, laptop bag, diaper bag" which are limited by size only according to the LATAM website. On our aircraft people brought small soft-sided day bags/large purses, camera bags, and small backpacks. I carried a man-purse (camera bag). Just be aware that if it is too big they may make you check it for which you will pay a charge.
If you meet the airlines' weight and size limits on checked (and carry-on) luggage, but are just a tad over some Tauck-only limitation you'll be fine. I don't see size restriction in the Before You Go > Luggage Handling and Restrictions on the Tauck website, is it spelled out in your Green Book?