I can easily update your shop from opencart 1.5.6.4 to opencart 2.3 with same data like customer, products, category etc.
Relevant Skills and Experience
Working from last 5 years on Opencart. Created more than 500+ opencart shop and extension. Please check my review
Proposed Milestones
$100 USD - Initial Milesotne
$100 USD - Complete Milestone
Additional Services Offered
$50 USD - Will create some banner also if needed
Which theme you are using on your current shop? How many 3rd party extension you have?