Got this info via email -

Top up now at https://onlinetopup.digicelgroup.com/Jamaica with JMD$1500 or more and we’ll give you twice the credit at no extra cost.

Offer available 12:00AM April 1st to 11:59PM April 30th. Bonus airtime will expire seven (7) days after being applied. Bonus airtime is valid for calls to the USA, Canada, UK landlines, Spain landlines, China, Hong Kong & Jamaican Digicel to Digicel calls only and does not apply to 4G broadband top ups. Terms & conditions apply.

QUICK TIP: To view your bonus credit balance dial *120*6# and press 'SEND'

If I am reading this right, I'll basically have ~$3700 total credits for $1500... and the bonus is good for Int'l.
Sounds good to me.