Hello,
Capital Gain would be around Rs. 18.76 Lakhs, assuming the date of purchase of the first property being sold as 31st Oct 2015.
Exemption from capital gain on sale of house property is available under Sec 54, where investment made in new house property before 1 year from the date of sale of the property is allowed as a deduction from the capital gain.
In your case, the new house property(second) is purchased on 24th Oct 2018, therefore to be eligible for the exemption you need to sale the first property up to 23rd Oct 2019. Till now you have only made the sale agreement, which doesn't constitute transfer since the whole payment is not received yet for the property.
I hope that this answer satisfies your requirements.
Regards,
CA Hunny Badlani