Using the Classical Malthusian Model for population growth which uses the population of each previous generation (Pt) and a growth rate (r) to derive the next generations population (Pt+1). The equation takes the form:

Pt+1 = r * Pt

Assuming couples had babies around age 16 and on average had 3 babies per couple (r=1.5) we get the following data:

Generation Population Year

1 70 16

2 105 32

3 158 48

4 236 64

5 354 80

6 532 96

7 797 112

8 1,196 128

9 1,794 144

10 2,691 160

11 4,037 176

12 6,055 192

13 9,082 208

14 13,623 224

15 20,435 240

16 30,653 256

17 45,979 272

18 68,968 288

19 103,452 304

20 155,179 320

21 232,768 336

22 349,152 352

23 523,728 368

24 785,592 384

25 1,178,388 400

26 1,767,582 416

27 2,651,373 432

So I would say that yes it is possible to grow that fast. Over 27 generations with a 1.5 growth rate the population of 70 would reach 2.6 Million.

I have attached the excel file with the data.