New mobile within 12k budget for dad

Hey guys, I'm looking for a new mobile for my dad. He is using an iPhone 5c and is in need for a secondary smartphone in around 10-12k budget. Camera quality is not an issue but he needs a phone which is slim and fast and which wont lag on normal usage. There are no other requirements as such.

I'm filling the questionnaire for a simple overview of my needs.
1. Budget- 10-12k
2. Display type and size- Good sunlight visiblity and 4 inches preferred and not more than 4.5 inches
3. Form Factor- Bar and slim mobile
4. Preferred choice of brand- Any reputed brands
5. Preferred input method- Touchscreen
6. What camera option you want- Flash needed and mega pixels doesn't matter.
7. Preferred operating system- Windows, Android
8. Preferred connectivity options- All possible options
9. Preferred applications- Not really but GPS is must
10. Primary use of handsetSecondary mobile with only calling and whatsapp mostly used
11. Any specific mobile phones in consideration- Lumia 525 or Lumia 630 currenty
12. Any other info that you want to share-

Requirement 1: Slim and Sleek mobile
Requirement 2: Good signal reception,
Requirement 3: Good battery and
Requirement 4: Lagless operation

I am planning to make the purchase in next 1 week. Can't wait any more for any other new models.